Biochemical studies of the last several years have shown that transport and mobilization of iron by microorganisms takes place using very powerful low-molecular-weight chelating agents. These compounds, called siderophores or siderochromes, are manufactured by bacteria and other organisms, as needed, to extract iron from their solution environment. The siderophores all form complexes containing high-spin ferric ion. Such complexes in aqueous solution are kinetically labile, with both ligand exchange and isomerization processes taking place rapidly with respect to the rate of iron uptake. It is the goal of this research to prepare, characterize and utilize kinetically-inert, metal-substituted complexes of the siderophores. These can then be used both as biological probes and as chemical probes. In the first type of application the uptake of the metal-substituted complexes is followed and its transport kinetics are compared to those of the natural iron-containing siderophore. In the second type of application the spectroscopic properties of the metal-substituted complexes are used to characterize the structure of the siderophore at the metal center. BIBLIOGRAPHIC REFERENCES: Kamal Abu-Dari and Kenneth N. Raymond, "Coordination Isomers of Biological Iron Transport Compounds. VII. The Preparation and Resolution of Tris(thiobenzohydroxamate)-chromium(III),-cobalt(III) and High-Spin -iron(III) Complexes," Inorg. Chem., (1977). Kamal Abu-Dari and Kenneth N. Raymond, "Coordination Isomers of Biological Iron Transport Compounds. VIII. The Resolution of Tris(hydroxamato) and Tris(thiohydroxamato) Complexes of High-Spin Iron(III)," J. Am. Chem. Soc., (1977).